1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a pack type battery having an improved covering.
2. Description of the Prior Art
Exemplary secondary batteries, also known as rechargeable batteries, may include nickel-hydrogen (Ni-MH) batteries or lithium ion batteries, classified according to their electrode active materials. Exemplary lithium ion batteries are liquid electrolyte batteries, solid polymer electrolyte batteries, and batteries using a gel phase electrolyte. Secondary batteries may be encased in various housings, such as a can or a pouch.
Lithium ion batteries have higher energy density per unit weight than primary, or non-rechargeable, batteries so relatively lightweight batteries can be manufactured. Additionally, lithium ion batteries are environmentally-friendly because heavy metals such as cadmium or mercury are not used, and such batteries can be charged and discharged more than 1000 times under normal conditions. Accordingly, lithium ion batteries have become highly developed with the development of recent information and communication technology.
Conventional lithium ion batteries are assembled by inserting an electrode assembly, including a wound positive electrode plate, negative electrode plate and separator, and electrolyte into a metal can, and sealing an opening of the can. Lithium ion batteries usually include an external electrode terminal insulated from the can. The electrode terminal serves as either a positive electrode or a negative electrode, and the can serves as the opposite electrode.
The secondary battery may malfunction due to a rapid voltage increase caused by an electrical short occurring by, an external impact on the battery or over-charge or over-discharge of the battery. Safety devices, such as a positive temperature coefficient (PTC) device, a thermal fuse, or a protection circuit module (PCM), may be coupled to the battery, thereby allowing the battery to be safely distributed and used in a pack.
Exemplary battery packs include hard pack batteries, typically having an integrally molded plastic resin housing, and inner pack batteries, wherein the housing is not separately molded and the batteries are primarily finished by a separate exterior decorating material such as a label. Inner pack batteries are sometimes less reliable because the label may detach from the inner pack battery. However, inner pack batteries are advantageous because they can be used regardless of shape and structure of an external device.
In one type of inner pack battery, a prismatic type can houses the electrode assembly. The PCM is installed on one side of the bare cell, and the PCM and the bare cell are coupled to a lead plate. A resin molding is used to cover the PCM and upper and lower surfaces of the bare cell.
The resin cover may include a skirt covering the upper and lower surfaces of the bare cell. The surface of the can and the skirt form a step on a side surface of the bare cell. The bare cell combined with the resin cover is then wrapped by the label. If the label is wrapped around the step, the label may be attached unevenly causing wrinkles that are not only aesthetically unappealing, but may also result in poor adhesion of the label. In some cases, insulating tape is attached to the side surface of the bare cell to compensate for the step. However, the use of insulation tape to compensate for the step increases manufacturing costs and manufacturing complexity.